This invention relates generally to visual testing apparatus. More particularly, the invention relates to improved apparatus for and a novel method of testing vision to detect any latency differences in optic nerve conduction between the two eyes of a person being tested. The improved apparatus and method of the present invention are particularly useful in detecting demyelinating diseases like multiple sclerosis which cause pathological changes in the optic nerve in a large percentage of cases.
The importance of optic nerve evaluation in diseases like mulitple sclerosis has led to the development of several electrophysiological tests including flicker fusion and visually evoked potentials. Flicker fusion requires the patient to identify the frequency at which a single strobing (flickering) light appears no longer to flicker. Flicker fusion has not found widespread acceptance because of the large number of false positives and false negatives which result from the rather wide spectrum of normal values. In contrast, visually evoked potentials have been generally accepted because they correctly identify optic nerve pathology in approximately 90% of confirmed cases of multiple sclerosis. To obtain visually evoked potentials, however, relatively expensive equipment and specially trained individuals to conduct and interpret the tests are required. Testing by visually evoked potentials, therefore, has a somewhat limited market.
The optic latency device and method of the present invention have the following advantages over the prior art. They reliably detect differences in the optic nerve conduction between the two eyes of a patient with demyeliating optic nerve disease. False positives and negatives are rare. The apparatus can be designed for mass distribution in a form that is easily portable and relatively inexpensive. The apparatus can also be operated successfully by a technician after only a few minutes of instruction. While the optic latency apparatus of the present invention provides more limited data than the apparatus for providing visually evoked potentials, it should find a wider utilization as a preliminary screening test.